In various well drilling operations it is desirable to estimate the location of a nearby wellbore. Examples of such operations include well intercept, well avoidance, well twinning, and relief well drilling operations.
Both passive and active magnetic ranging techniques are known in the oil field services industry. For example, U.S. Pat. Nos. 6,985,814 and 7,656,161 to McElhinney, disclose passive ranging methodologies for use in well twinning applications. The '814 patent makes use of remanent magnetization in a target well casing string while the '161 patent teaches a method for magnetizing the target well casing string prior to deployment in the target well.
U.S. Pat. No. 7,812,610 to Clark teaches a methodology in which a secondary electrical current is induced in the target wellbore casing string, e.g., via inducing a voltage across an insulative gap in the drill string located in the drilling wellbore. The secondary current in the target wellbore casing string further induces a magnetic field that may be measured in the drilling wellbore and used to estimate the location of the target. However, the need to stop drilling and make magnetic field measurements at three or more tool face angles can result in a time consuming drilling process. Further improvement is required.